Negative electrode material for secondary battery with non-aqueous electrolyte, method for manufacturing negative electrode material for secondary battery with non-aqueous electrolyte, and lithium ion secondary battery

ABSTRACT

The present invention is a method for manufacturing a negative electrode material for a secondary battery with a non-aqueous electrolyte comprising at least: coating a surface of powder with carbon at a coating amount of 1 to 40 mass % with respect to an amount of the powder by heat CVD treatment under an organic gas and/or vapor atmosphere at a temperature between 800° C. and 1300° C., the powder being composed of at least one of silicon oxide represented by a general formula of SiO x  (x=0.5 to 1.6) and a silicon-silicon oxide composite having a structure that silicon particles having a size of 50 nm or less are dispersed to silicon oxide in an atomic order and/or a crystallite state, the silicon-silicon oxide composite having a Si/O molar ratio of 1/0.5 to 1/1.6; blending lithium hydride and/or lithium aluminum hydride with the powder coated with carbon; and thereafter heating the powder coated with carbon at a temperature between 200° C. and 800° C. to be doped with lithium at a doping amount of 0.1 to 20 mass % with respect to an amount of the powder. As a result, there is provided a method for manufacturing a negative electrode material for a secondary battery with a non-aqueous electrolyte that enables a silicon oxide negative electrode material superior in first efficiency and cycle durability to conventional ones to be mass-produced (manufactured) readily and safely even in an industrial scale.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a negative electrode material for asecondary battery with a non-aqueous electrolyte, such as a lithium ionsecondary battery, to a method for manufacturing the same, and to alithium ion secondary battery by using the same, and the material iscomposed of a silicon-silicon oxide-lithium composite useful for thenegative electrode material for a secondary battery with a non-aqueouselectrolyte.

2. Description of the Related Art

Currently lithium ion secondary batteries are widely used for mobileelectronic devices, such as a mobile phone, a laptop computer, and thelike, because of high energy density. In recent years, with increasingawareness of environmental issues, an attempt to use this lithium ionsecondary battery as a power source for an electric automobile, which isan environmentally-friendly automobile, has become active.

However, the performance of a current lithium ion secondary battery isinsufficient for application to the electric automobile in terms ofcapacity and cycle durability. There has been accordingly advanceddevelopment of a next generation model of the lithium ion secondarybattery that has high capacity and is superior in cycle durability.

As one problem of the development of the next generation model of thelithium ion secondary battery, improvement in the performance of anegative electrode material is pointed out.

Currently carbon negative electrode materials are widely used. Thedevelopment by using a material other than carbon has also advanced tosharply enhance the performance, and a representative thereof is siliconoxide.

The silicon oxide has several times as much theoretical capacity ascarbon has, and there is thereby possibility that silicon oxide becomesan excellent negative electrode material.

There were, however, problems such as low first efficiency, lowelectronic conductivity, and low cycle durability at the beginning ofthe development, and various improvements have accordingly made so far.

Here, the first efficiency means a ratio of discharge capacity to chargecapacity in the first charge/discharge. As a result of the low firstefficiency, the energy density of the lithium ion secondary batterydecreases. It is considered that the low first efficiency of siliconoxide is caused by generating a lot of lithium compounds that do notcontribute to the charge/discharge at the first charge.

As a method to solve this, there has been known a method of generatingthe above-described lithium compounds by making silicon oxide andlithium metal or a lithium compound (lithium oxide, lithium hydroxide,lithium hydride, organolithium, and the like) react an advance, beforethe first charge.

For example, Patent Literature 1 discloses use of a silicon oxide thatcan occlude and release lithium ions as a negative electrode activematerial, and a negative electrode material that satisfies a relation ofx>0 and 2>y>0 wherein a ratio of the number of atoms among silicon,lithium, and oxygen contained in the silicon oxide is represented by1:x:y.

As a method for manufacturing the above-described silicon oxide that isrepresented by a compositional formula of Li_(x)SiO_(y) and containslithium, there is disclosed a method in which a suboxide of siliconSiO_(y) that does not contain lithium is synthesized in advance, andlithium ions are occluded by an electrochemical reaction between theobtained suboxide of silicon SiO_(y) and lithium or a substancecontaining lithium. In addition, there is disclosed a method in which asimple substance of each of lithium and silicon, or a compound thereofare blended at a predetermined molar ratio, and it is heated under anon-oxidizing atmosphere or an oxygen-regulated atmosphere tosynthesize.

It describes that as a starting raw material, each of oxides andhydroxides, salts such as carbonates and nitrates, organolithiums, andthe like are exemplified, and although it is normally possible tosynthesize at a heating temperature of 400° C. or more, a temperature of400 to 800° C. is preferable, since a disproportionation reaction tosilicon and silicon dioxide may occur at a temperature of 800° C. ormore.

Moreover, Patent Literatures 2 to 4 describe that a chemical method oran electrochemical method is used as a method for preliminarilyinserting lithium before storing the negative electrode active materialin a battery container.

It describes that as the chemical method, a method of making thenegative electrode active material directly react with lithium metal, alithium alloy (lithium-aluminum alloy and the like), or lithiumcompounds (n-butyllithium, lithium hydride, lithium aluminum hydride,and the like), and a lithium insertion reaction is preferably performedat a temperature of 25 to 80° C. in the chemical method. Moreover, itdiscloses, as the electrochemical method, a method of discharging, atopen system, oxidation reduction system in which the above-describednegative electrode active material is used for a positive electrodeactive material and a non-aqueous electrolyte containing lithium metal,a lithium alloy, or a lithium salt is used for a negative electrodeactive material, and a method of charging oxidation reduction systemthat is composed of a non-aqueous electrolyte that contains a transitionmetal oxide containing lithium, the negative electrode active material,and a lithium salt, as the positive electrode active material.

Moreover, Patent Literature 5 discloses powder of silicon oxidecontaining lithium represented by a general formula of SiLi_(x)O_(y), inwhich the ranges of x and y are 0<x<1.0 and 0<y<1.5, lithium is fused,and a part of the fused lithium is crystallized. It also discloses amethod for manufacturing the powder of the silicon oxide containinglithium, in which a mixture of raw material powder that generates SiOgas and metallic lithium or a lithium compound is made to react byheating under an inert gas atmosphere or under reduced pressure at atemperature of 800 to 1300° C.

It discloses that, at this point in time, silicon oxide (SiO_(x)) powder(0<z<2) and silicon dioxide powder can be used as the raw materialpowder that generates SiO gas, and it is used after adding reductionpowder (metallic silicon compounds, and powder containing carbon) asneeded. It also discloses that the metallic lithium and the lithiumcompounds are not restricted in particular, and as the lithiumcompounds, for example, lithium oxide, lithium hydroxide, lithiumcarbonate, lithium nitrate, lithium silicate, hydrates thereof, or thelike can be used, other than the metallic lithium.

On the other hand, when electronic conductivity is low, the capacity ofthe lithium ion secondary battery under high load decreases, andparticularly cycle durability decreases.

For improvement to enhance this electronic conductivity, PatentLiterature 6 discloses a negative electrode material having anelectronic conductive material layer formed on a surface of siliconoxide particles. It describes that the silicon oxide among them issilicon oxide having an elementary composition of Si and O, and ispreferably a suboxide of silicon represented by SiO_(x) (0<x<2), andthat it can be lithium silicate in which silicon oxide is doped with Li.It also describes that a carbon material is preferably used for aconductive material and it can be manufactured by using a CVD method, aliquid phase method, or a sintering method.

Moreover, as one improving method to enhance the cycle durability, thatis, to suppress an occurrence of a decrease in the capacity even whencharge/discharge are repeated, Patent Literature 7 discloses aconductive silicon composite in which a diffraction peak attributable toSi (111) is observed when x-ray diffraction, the size of silicon crystalobtained by the Scherrer method based on the half-width of a diffractionline thereof is 1 to 500 nm, and a surface of its particle is coatedwith carbon, the composite having a structure that crystallites ofsilicon are dispersed to a silicon compound, particularly, theconductive silicon composite in which the silicon compound is silicondioxide and at least a part of the surface thereof is adhered to carbon.

There is an example of a method for manufacturing this composite inwhich silicon oxide is subjected to disproportionation with an organicgas and/or vapor at a temperature of 900 to 1400° C., and carbon isdeposited by chemical vapor deposition treatment.

Moreover, for improvement in both of the first efficiency and cycledurability, Patent Literature 8 discloses a silicon-silicon oxidecomposite doped with lithium, the composite having a structure thatsilicon particles having a size of 0.5 to 50 nm are dispersed to siliconoxide in an atomic order and/or a crystallite state, particularly, aconductive silicon-silicon oxide-lithium composite in which the surfacethereof is coated with carbon at a coating amount of 5 to 50 mass % withrespect to an amount of the whole composite particles after surfacetreatment.

It describes a method for manufacturing this composite, the method inwhich silicon oxide is a lithium dopant and lithium metal and/or anorganolithium compound is used to dope with lithium at a temperature of1300° C. or less, and further a method in which a silicon-siliconoxide-lithium composite that is pulverized into a predetermined particlesize is subjected to heat CVD with an organic hydrocarbon gas and/orvapor at a temperature of 900 to 1400° C. and a carbon coating is formedat a coating amount of 5 to 50 mass % with respect to an amount of thewhole composite particles after surface treatment.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 2997741-   Patent Literature 2: Japanese Unexamined Patent publication (Kokai)    No. 8-102331-   Patent Literature 3: Japanese Unexamined Patent publication (Kokai)    No. 8-130011-   Patent Literature 4: Japanese Unexamined Patent publication (Kokai)    No. 8-130036-   Patent Literature 5: Japanese Unexamined Patent publication (Kokai)    No. 2003-160328-   Patent Literature 6: Japanese Unexamined Patent publication (Kokai)    No. 2002-42806-   Patent Literature 7: Japanese Patent No. 3952180-   Patent Literature 8: Japanese Unexamined Patent publication (Kokai)    No. 2007-294423

SUMMARY OF THE INVENTION

As described above, the silicon oxide negative electrode material hasbeen improved. However, even the most advanced art described in PatentLiterature 8 is still insufficient for practical use.

That is, the conductive silicon-silicon oxide-lithium compositemanufactured by the method described in Patent Literature 8 hasconsequently achieved extensive improvement in terms of the firstefficiency but the cycle durability thereof is inferior in comparisonwith a conductive silicon-silicon oxide composite that is not doped withlithium.

Moreover, in another aspect, the method by using lithium metal and/or anorganolithium compound as the lithium dopant makes both of reaction heatand a reaction rate high, and thereby there arises problems that it ishard to control reaction temperature, and to manufacture it in anindustrial scale.

The present invention was accomplished in view of the aforementionedproblems, and it is an object of the present invention to provide anegative electrode material for a secondary battery with a non-aqueouselectrolyte, with which a silicon oxide negative electrode materialsuperior in first efficiency and cycle durability to conventional onescan be mass-produced (manufactured) readily and safely even in anindustrial scale, a method for manufacturing the same, and a lithium ionsecondary battery using the same.

In order to accomplish the above object, the present invention providesa negative electrode material for a secondary battery with a non-aqueouselectrolyte including at least: a silicon-silicon oxide composite havinga structure that silicon particles having a size of 0.5 to 50 nm aredispersed to silicon oxide in an atomic order and/or a crystallitestate, the silicon-silicon oxide composite having a Si/O molar ratio of1/0.5 to 1/1.6; and a carbon coating formed on a surface of thesilicon-silicon oxide composite at a coating amount of 1 to 40 mass %with respect to an amount of the silicon-silicon oxide composite,wherein at least the silicon-silicon oxide composite is doped withlithium at a doping amount of 0.1 to 20 mass % with respect to an amountof the silicon-silicon oxide composite, and a ratio I(SiC)/I(Si) of apeak intensity I(SiC) attributable to SiC of 2θ=35.8±0.2° to a peakintensity I(Si) attributable to Si of 2θ=28.4±0.2° satisfies a relationof I(SiC)/I(Si)≦0.03, when x-ray diffraction using Cu—Kα ray.

In this manner, the negative electrode material for a secondary batterywith a non-aqueous electrolyte, wherein, in the silicon-silicon oxidecomposite that is doped with lithium and has the carbon coating formedthereon, the ratio I(SiC)/I(Si) of the peak intensity I(SiC)attributable to SiC of 2θ=35.8±0.2° to the peak intensity I(Si)attributable to Si of 2θ=28.4±0.2° satisfies the relation ofI(SiC)/I(Si)≦0.03, when x-ray diffraction using Cu—Kα ray, can has asufficiently low amount of SiC at an interface between thesilicon-silicon oxide composite and the carbon coating, and thereby hasgood electronic conductivity and discharge capacity, and particularlygood cycle durability when used for a negative electrode material.

In addition, the negative electrode material is based on thesilicon-silicon oxide composite which is doped with lithium at a dopingamount of 0.1 to 20 mass % with respect to an amount of thesilicon-silicon oxide composite, which has the structure that siliconparticles having a size of 0.5 to 50 nm and having the carbon coatingformed thereon at a coating amount of 1 to 40 mass % are dispersed tosilicon oxide in an atomic order and/or a crystallite state, and whichhas a Si/O molar ratio of 1/0.5 to 1/1.6, and thereby has highercapacity and higher cycle durability in comparison with conventionalones and is superior in particularly the first efficiency.

In this case, a peak attributable to lithium aluminate can be furtherobserved in the negative electrode material for a secondary battery witha non-aqueous electrolyte, when the x-ray diffraction using Cu—Kα ray.

The above-described negative electrode material containing aluminum canalso has a sufficiently low amount of SiC at the interface between thesilicon-silicon oxide composite and the carbon coating, and thereby issuperior in, particularly, the cycle durability and the firstefficiency. As described later, lithium aluminum hydride containingaluminum is preferably used for doping with lithium.

Furthermore, the present invention provides a lithium ion secondarybattery having at least a positive electrode, a negative electrode, anda non-aqueous electrolyte having lithium ion conductivity, wherein thenegative electrode material for a secondary battery with a non-aqueouselectrolyte described in the present invention is used for the negativeelectrode.

As described above, the negative electrode material for a secondarybattery with a non-aqueous electrolyte according to the presentinvention enables good battery characteristics (the first efficiency andthe cycle durability) when used for a negative electrode of anon-aqueous electrolyte secondary battery. The lithium ion secondarybattery in which the negative electrode material for a secondary batterywith a non-aqueous electrolyte according to the present invention isused is therefore superior in the battery characteristics, particularly,the first efficiency and the cycle durability.

Furthermore, the present invention provides a method for manufacturing anegative electrode material for a secondary battery with a non-aqueouselectrolyte including at least: coating a surface of powder with carbonat a coating amount of 1 to 40 mass % with respect to an amount of thepowder by heat CVD treatment under an organic gas and/or vaporatmosphere at a temperature between 800° C. and 1300° C., the powderbeing composed of at least one of silicon oxide represented by a generalformula of SiO_(x) (x=0.5 to 1.6) and a silicon-silicon oxide compositehaving a structure that silicon particles having a size of 50 nm or lessare dispersed to silicon oxide in an atomic order and/or a crystallitestate, the silicon-silicon oxide composite having a Si/O molar ratio of1/0.5 to 1/1.6; blending lithium hydride and/or lithium aluminum hydridewith the powder coated with carbon; and thereafter heating the powdercoated with carbon at a temperature between 200° C. and 800° C. to bedoped with lithium at a doping amount of 0.1 to 20 mass % with respectto an amount of the powder.

In the case of coating with carbon by the heat CVD treatment afterdoping with lithium, silicon and carbon at the interface between thesilicon-silicon oxide composite and the carbon coating react toaccelerate generation of SIC due to the doping lithium, crystallizationof silicon contained in the silicon-silicon oxide composite isaccelerated, and thereby the electronic conductivity and cycledurability of the negative electrode material to be obtained in thiscase are not good. On the other hand, doping with lithium after coatingwith carbon as described above enables a sufficiently low amount of thegeneration of SIC at the interface between the silicon-silicon oxidecomposite and the carbon coating. In addition to this, it can besuppressed to excessively grow silicon crystal contained in thesilicon-silicon oxide composite, and the negative electrode material canbe manufactured which enables good battery characteristics, such ascycle durability, when used for a negative electrode.

Moreover, when the silicon-silicon oxide composite is coated with carbonand doped with lithium, the capacity thereof can be improved incomparison with conventional methods, and the negative electrodematerial for a secondary battery with a non-aqueous electrolyte can bemanufactured which has improved conductivity and first efficiency.

Moreover, when the temperature of the heat CVD treatment is between 800°C. and 1300° C., crystallization of carbon contained in the carboncoating and bonding of the carbon coating and the silicon-silicon oxidecomposite can be promoted, a fine carbon coating with high quality canbe formed with high productivity, and the negative electrode materialfor a secondary battery with a non-aqueous electrolyte can bemanufactured which has higher capacity and is superior in the cycledurability.

Furthermore, when lithium hydride and/or lithium aluminum hydride isused as the lithium dopant, the reaction is milder in comparison withthe case of using lithium metal as the lithium dopant, and it can bedoped with lithium with readily controlling the temperature. Inaddition, silicon oxide can be more reduced in comparison with the caseof using a dopant containing oxygen, such as lithium hydroxide andlithium oxide, the negative electrode material having high dischargecapacity can be thereby manufactured, and it can be a method formanufacturing a high capacity negative electrode material suitable toindustrial mass production.

When the powder is heated at a low temperature between 200° C. and 800°C. to be doped with lithium, SiC can be prevented from being generated,the silicon crystal contained in the silicon-silicon oxide composite canbe prevented from excessively growing, and thereby the dischargecapacity and the cycle durability can be surely prevented fromdeteriorating.

As explained above, the present invention provides the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte, with which a silicon oxide negative electrode materialsuperior in first efficiency and cycle durability to conventional onescan be mass-produced (manufactured) readily and safely even in anindustrial scale, a method for manufacturing the same, and a lithium ionsecondary battery using the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an x-ray diffraction chart of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte in Example 1.

FIG. 2 is a view showing an x-ray diffraction chart of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte in Example 2.

FIG. 3 is a view showing an x-ray diffraction chart of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte in Comparative Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be explained in more detail.

In order to achieve the above object, the present inventor hasrepeatedly keenly conducted studies on the problems of a conventionalnegative electrode material for a secondary battery with a non-aqueouselectrolyte and on the solution thereof.

The present inventor has thoroughly inspected the problem of the artdescribed in Patent Literature 8, which is the most advanced art amongthem, and discovered the cause of inferior electronic conductivity andcycle durability.

That is, the present inventor has found that in the conductivesilicon-silicon oxide-lithium composite manufactured by the methoddisclosed in Patent Literature 8, the carbon coating is apt to changeinto SiC and the silicon is apt to crystallize when the heat CVDtreatment with high heat is performed after the doping with lithium, andthat this is caused by the doping with lithium.

The mechanism is not quite clear. It can be, however, considered that apart of silicon oxide is reduced by lithium and becomes silicon duringthe doping with lithium by using lithium metal and/or organolithiumcompounds, this silicon is apt to change into SiC and to crystallize ascompared with silicon generated by the disproportionation, and causesdeterioration of the battery characteristics, particularly, the cycledurability and the discharge capacity, when used for a negativeelectrolyte.

The present inventor further has repeatedly keenly conducted studiesbased on the above result of the studies, and consequently found thatperforming the heat CVD treatment before the doping with lithium isnecessary to suppress the change into SiC, and that an upper limittemperature of 800° C. during the doping with lithium is necessary tostrongly suppress the crystallization of silicon, the upper limittemperature of 800° C. which is lower than an upper limit temperature of900° C. at which silicon oxide without doping lithium does notcrystallize.

Moreover, the present inventor has keenly conducted also studies on alithium dopant.

That is, in the case of using a lithium dopant containing oxygen, suchas lithium hydroxide and lithium oxide, like a conventional case,instead of lithium metal and/or an organolithium compound, there arisesa problem that silicon oxide cannot be reduced due to oxygen containedin its composition, and that the discharge capacity thereby decreases,although the reaction is mild. In the case of using metallic lithium,there arises a problem that an ignited state is created due to intensereaction, and that it is thereby hard to control the reaction. Thepresent inventor accordingly has repeatedly keenly conducted studies ona method for solving these problems.

As a result, the present inventor has found that when lithium hydride orlithium aluminum hydride is used as the lithium dopant and it is heatedat a temperature between 200° C. and 800° C., the equivalent of thecapacity in the case of using lithium metal and/or the organolithiumcompound can be obtained, the reaction is mild, thereby the temperaturecan be readily controlled, and doping with lithium can be performed inan industrial scale.

The present inventor has found, based on the above result of thestudies, that in the event that after coating, with carbon, the surfaceof silicon oxide or the composite that is constituted by siliconparticles being dispersed to silicon oxide, lithium hydride and/orlithium aluminum hydride as the lithium dopant is added thereto and theyare heated at a temperature between 200° C. and 800° C., the reaction ismild, thereby the temperature can be readily controlled, and the dopingwith lithium can be readily performed in an industrial scale with thechange into SiC and the crystallization suppressed. The present inventorhas also found that use of the above-described negative electrodematerial as a negative electrode active material of the secondarybattery with a non-aqueous electrolyte, such as the lithium ionsecondary battery, enables the secondary battery with a non-aqueouselectrolyte having higher capacity, higher first efficiency, andsuperior cycle durability in comparison with conventional methods to beobtained. The present inventor thereby brought the present invention tocompletion.

Hereinafter, the present invention will be explained in detail withreference to the drawings. However, the present invention is notrestricted thereto.

The negative electrode material for a secondary battery with anon-aqueous electrolyte according to the present invention comprises atleast: the silicon-silicon oxide composite having the structure thatsilicon particles having a size of 0.5 to 50 nm are dispersed to siliconoxide in an atomic order and/or a crystallite state, the silicon-siliconoxide composite having a Si/O molar ratio of 1/0.5 to 1/1.6; and thecarbon coating formed on the surface of the silicon-silicon oxidecomposite at a coating amount of 1 to 40 mass % with respect to anamount of the silicon-silicon oxide composite.

In this negative electrode material, at least the silicon-silicon oxidecomposite is doped with lithium at a doping amount of 0.1 to 20 mass %with respect to an amount of the silicon-silicon oxide composite, andthe ratio I(SiC)/I(Si) of the peak intensity I(SiC) attributable to SiCof 2θ=35.8±0.2° to the peak intensity I(Si) attributable to Si of2θ=28.4±0.2° satisfies the relation of I(SiC)/I(Si)≦0.03, when the x-raydiffraction using Cu—Kα ray.

For example, it is a conductive silicon-silicon oxide-lithium compositehaving the carbon coating formed thereon. The negative electrodematerial is composed of the silicon-silicon oxide composite that has afine structure that silicon particles having a size of 0.5 to 50 nm aredispersed to silicon oxide and/or lithium silicate in an atomic orderand/or a crystallite state and has superior conductivity due to thecarbon coating, superior first efficiency due to the doping withlithium, larger discharge capacity than conventional ones, and goodcycle durability. It is to be noted that this dispersion structure canbe observed by a transmission electron microscope.

Moreover, the ratio of the peak intensity I(SiC) attributable to SiC of2θ=35.8±0.2° to the peak intensity I(Si) attributable to Si of2θ=28.4±0.2° satisfies the relation of I(SiC)/I(Si)≦0.03, when x-raydiffraction using Cu—Kα ray.

This I(SiC)/I(Si) can be used as a criterion of the change of the carboncoating into SiC. In the case of I(SiC)/I(Si)>0.03, too many parts arechanged into SiC in the carbon coating, and this may make a negativeelectrode material inferior in electronic conductivity and dischargecapacity, because the generation of a large amount of SiC causes adecrease in the electronic conductivity of the interface and of thecarbon coating, the capacity of the lithium ion secondary battery underhigh load consequently decreases, and particularly the cycle durabilitydecreases. However, generating a very thin SiC layer at the interfacebetween the carbon coating and the silicon-silicon oxide composite isuseful for enhancing the adhesion strength of the coating.

The battery characteristics are therefore significantly deteriorated inthe case of I(SiC)/I(Si)>0.03, whereas it is sufficiently permissible tobe the amount of generated SiC under a condition of satisfying therelation of I(SiC)/I(Si)≦0.03, when x-ray diffraction using Cu—Kα ray.The negative electrode material for a secondary battery with anon-aqueous electrolyte according to the present invention accordinglysatisfies I(SiC)/I(Si)≦0.03.

In this case, the size of the silicon particles is defined by the size Dof a silicon crystallite, obtained by the Scherrer formula (1) based onthe full width at half maximum of a diffraction peak of Si (111) inx-ray diffraction.

D(nm)=Kλ/B cos θ  (1)

Here, K=0.9, λ=0.154 nm (in case of Cu—Kα), B=full width at half maximum(rad), θ=peak position (°).

The size of the silicon particles is desirably 0.7 to 40 nm, moredesirably 1 to 30 nm.

When the particle size is 0.5 nm or more, the first efficiency can beprevented from decreasing. When the particle size is 50 nm or less, thecapacity and the cycle durability can be prevented from decreasing.

Moreover, in the negative electrode material for a secondary batterywith a non-aqueous electrolyte according to the preset invention, amolar ratio of Si/O contained in the silicon-silicon oxide-lithiumcomposite is 1/0.5 to 1/1.6. When the molar ratio of oxygen to siliconis 0.5 or more, the cycle durability can be prevented from decreasing.When the molar ratio is 1.6 or less, the capacity can be prevented fromdecreasing.

A silicon content is desirably 10 to 60 mass %, particularly 15 to 50mass %, more particularly 20 to 40 mass %. A silicon oxide content isdesirably 40 to 90 mass %, particularly 50 to 85 mass %, moreparticularly 60 to 80 mass %.

Moreover, the doping amount of lithium with respect to the amount of thesilicon-silicon oxide composite is 0.1 to 20 mass %, desirably 0.5 to 17mass %, more desirably 1 to 15 mass %.

When a lithium content is 0.1 mass % or more, the first efficiency canbe improved. When a lithium content is 20 mass % or less, there arisesno problem of a decrease in the cycle durability and of handling safety.

It is to be noted that the carbon coating may be doped with lithium atthe same time, and the content is not restricted in particular.

Moreover, an average particle size of the negative electrode materialfor a secondary battery with a non-aqueous electrolyte according to thepresent invention is desirably 1 to 50 μm, particularly 3 to 20 μm, whenit is measured as a cumulative weight average value (or median diameter)D₅₀ upon measurement of particle size distribution by laserdiffractometry.

The carbon coating amount is 1 to 40 mass % with respect to the amountof the silicon-silicon oxide composite coated with carbon, desirably 2to 30 mass %, more desirably 3 to 20 mass %.

When the carbon coating amount is 1 mass % or more, the conductivity canbe sufficiently improved. When the carbon coating amount is 40 mass % orless, a risk of a decrease in the discharge capacity due to too manyproportions of carbon can be avoided as much as possible.

The electrical conductivity of the silicon-silicon oxide-lithiumcomposite powder having the carbon coating formed thereon is desirably1×10⁻⁶ S/m or more, particularly 2×10⁻⁴ S/m or more.

When the electrical conductivity is 1×10⁻⁶ S/m or more, the conductivityof the electrode becomes low, and a risk of a decrease in the cycledurability can be reduced when used as a negative electrode material fora lithium ion secondary battery.

It is to be noted that the “electrical conductivity” as used herein is avalue obtained by filling a four-terminal cylindrical cell with powderto be measured and measuring a voltage drop at the time of conducting anelectric current through the powder.

Moreover, the peak attributable to lithium aluminate can be furtherobserved in the negative electrode material for a secondary battery witha non-aqueous electrolyte according to the present invention, when thex-ray diffraction using Cu—Kα ray. Moreover, the peak attributable tolithium silicate can be also observed in the negative electrodematerial.

Here, the lithium silicate means compounds represented by a generalformula of Li_(x)SiO_(y) (1≦x≦4, 2.5≦y≦4), and the lithium aluminatemeans compounds represented by a general formula of Li_(x)AlO_(y)(0.2≦x≦1, 1.6≦y≦2).

That is, the doping lithium can exist mainly in a state of lithiumsilicate and/or lithium aluminate in the negative electrode material fora secondary battery with a non-aqueous electrolyte, and thereby lithiumstably exists in the silicon-silicon oxide composite.

The negative electrode material according to the present invention canbe doped with lithium by using lithium aluminum hydride containingaluminum. This negative electrode material also has a sufficiently lowamount of SiC at the interface between the silicon-silicon oxidecomposite and the carbon coating and is superior in the cycle durabilityand the first efficiency.

Next, the method for manufacturing a negative electrode material for asecondary battery with a non-aqueous electrolyte according to thepresent invention will be explained in detail, but the method is ofcourse not restricted thereto.

First, powder is prepared which is composed of at least one of siliconoxide represented by a general formula of SiO_(x) (0.5≦x≦1.6), and thesilicon-silicon oxide composite having the structure that siliconparticles having a size of 50 nm or lass are dispersed to silicon oxidein an atomic order and/or a crystallite state, the composite having aSi/O molar ratio of 1/0.5 to 1.6.

It is to be noted that this powder can be pulverized and classified in adesired particle size distribution.

The surface of the powder is coated with carbon at a coating amount of 1to 40 mass % with respect to the amount of the powder by the heat CVDtreatment under an organic gas and/or vapor atmosphere at a temperaturebetween 800° C. and 1300° C., to give conductivity.

It is to be noted that the time of the heat CVD treatment isappropriately set according to the relation of the carbon coatingamount. In the event that the prepared powder contains silicon oxide,silicon oxide changes into a silicon-silicon oxide composite due to theinfluence of the treatment heat.

In the event that particles aggregate during the treatment, theaggregation can be disintegrated with a ball mill and the like. When theaggregation is disintegrated, the heat CVD treatment can be performedagain by the same way as above.

Specifically, the powder that is composed of at least one of siliconoxide and the silicon-silicon oxide composite is subjected to carboncoating treatment by heating to a temperature between 800° C. and 1300°C. (desirably between 900° C. and 1300° C., more desirably between 900°C. and 1200° C.) under an atmosphere containing at least an organic gasand/or vapor, by using a reactor that is heated at 800 to 1300° C. underinert gas flow.

As described above, when the temperature of the heat CVD treatment is800° C. or more, sufficient fusion between the carbon coating and thesilicon-silicon oxide composite, and sufficient alignment(crystallization) of carbon atom can be ensured. The negative electrodematerial for a secondary battery with a non-aqueous electrolyte that hashigher capacity and is superior in the cycle durability can be thereforeobtained. In addition, forming fine silicon crystal does not take longtime, and it is efficient. When the temperature of the heat CVDtreatment is 1300° C. or less, a risk of a deterioration in functions ofthe negative electrode material, which is caused by interfering withmigration of lithium ion due to the development of structured crystal ofa silicon dioxide part can be eliminated.

At this point in time, the silicon-silicon oxide composite powder havingthe carbon coating formed thereon has not been doped with lithium yet,in the present invention. The formation of SiC is thereby suppressedeven when the heat CVD treatment is performed at a high temperature of800° C. or more, particularly, 900° C. or more.

An organic material capable of producing carbon (graphite) by pyrolysisat the above-mentioned heat-treatment temperatures, particularly under anon-oxidative atmosphere, is preferably selected as an organic materialused for a raw material that generates the organic gas in the presentinvention.

Examples of such organic materials include hydrocarbon alone or amixture thereof, such as methane, ethane, ethylene, acetylene, propane,butane, butene, pentane, isobutane, hexane, and cyclohexane, andmonocyclic to tricyclic aromatic hydrocarbons or a mixture thereof, suchas benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane,naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene,cumarone, pyridine, anthracene, phenanthrene. Additionally, gas lightoils, creosote oils, anthracene oils, naphtha-cracked tar oils that areproduced in the tar distillation process can be used alone or as amixture.

As an apparatus for performing the heat CVD treatment, a reactor havinga mechanism for heating an object to be treated under a non-oxidizingatmosphere may be used and it is not restricted in particular.

For example, continuous or batch-wise treatment can be performed.Specifically, a fluidized bed reactor, a rotary furnace, a verticalmoving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln,and the like may be selected, depending on a particular purpose.

Moreover, lithium hydride and/or lithium aluminum hydride are blendedwith the powder coated with carbon.

This blending is not restricted in particular as long as an apparatusthat enables uniform blending under a dry atmosphere is used, and atumbler mixer is exemplified as a small apparatus.

Specifically, a predetermined amount of the silicon-silicon oxidecomposite powder having the carbon coating formed thereon and of powderof lithium hydride and/or lithium aluminum hydride is weighed out in aglove box under a dry air atmosphere to put into a stainless steelsealed container. They are rotated at room temperature for apredetermined time with them set to the tumbler mixer, and blended so asto be uniform.

Lithium hydride and/or lithium aluminum hydride is used as the lithiumdopant. When lithium hydride is used, the first efficiency is higher incomparison with the case of using lithium aluminum hydride having thesame mass amount, and use of lithium hydride is thus better from theviewpoint of the battery characteristics. Moreover, lithium hydride maybe used together with lithium aluminum hydride. Commercial lithiumaluminum hydride as a reducing agent is commonly circulated, and thuscan be easily obtained.

In the case of using metallic lithium and the like as the lithiumdopant, the reactivity of a lithium doping agent is too high, and it istherefore necessary to perform the blending under an inert gasatmosphere, such as argon, in addition to under a dry atmosphere. On theother hand, in the case of using lithium hydride and/or lithium aluminumhydride, like the present invention, the blending can be performed undera dry atmosphere only, and is remarkably easy to handle.

Moreover, in the case of using metallic lithium and the like, a chainreaction occurs, and there is a high risk to create an ignited state. Inthe ignited state, there is a problem that silicon crystal isexcessively grown, and the capacity and the cycle durability therebydecrease, in some cases. In case of lithium hydride and/or lithiumaluminum hydride, the reaction proceeds slowly, and an increase intemperature due to reaction heat is several dozen degrees. The ignitedstate is not therefore created in this case, and the negative electrodematerial that has high capacity and is superior in the cycle durabilitycan be readily manufactured in an industrial scale.

Moreover, in the case of using a dopant containing oxygen, such aslithium hydroxide and lithium oxide, there is a risk of the decrease inthe discharge capacity, which is caused by an insufficient reductionamount of silicon oxide of the manufactured negative electrode material.On the other hand, in the case of lithium hydride and/or lithiumaluminum hydride, like the present invention, such a risk can be surelyavoided, and the negative electrode material having high capacity can besurely manufactured.

It is to be noted that when unreacted lithium hydride or lithiumaluminum hydride is left behind, it is undesirable in both batterycharacteristic and safety aspects.

The lithiation reaction is solid-solid reaction between thesilicon-silicon oxide composite having the carbon coating formed thereonand the lithium dopant. However, since the rate of diffusion of lithiuminto a solid is generally low, it is difficult for lithium to penetratecompletely uniformly into the inside of the silicon-silicon oxidecomposite having the carbon coating formed thereon.

For safety sake, an additive amount of lithium is desirably equal to orless than an amount to supplement overall irreversible capacity (thedifference between the charge capacity and the discharge capacity at thefirst charge/discharge), that is, Li/O≦1. To achieve this, lithiumhydride or lithium aluminum hydride can be supplied in a powder or massform, but it is desirably used in a powder form as well as thesilicon-silicon oxide composite.

Thereafter, the powder coated with carbon is heated at a temperaturebetween 200° C. and 800° C. to be doped with lithium at a doping amountof 0.1 to 20 mass % with respect to the amount of the powder.

When the doping with lithium is performed at a temperature of 200° C. ormore, an insufficient reaction can be prevented. When the doping withlithium is performed at a temperature of 800° C. or less, the siliconcrystal contained in the silicon-silicon oxide composite can beprevented from excessively growing, and thereby the capacity under highload and particularly the cycle durability can be surely prevented fromdecreasing. That is, the negative electrode material for a secondarybattery with a non-aqueous electrolyte that has high capacity and issuperior in the cycle durability can be manufactured.

A reactor having a heating mechanism is preferably used for theabove-described lithiation reaction under an inert gas atmosphere, andthe detail thereof is not restricted in particular except for a heatingtemperature between 200° C. and 800° C.

For example, continuous or batch-wise treatment can be performed.Specifically, a rotary furnace, a vertical moving bed reactor, a tunnelfurnace, a batch furnace, a rotary kiln, and the like may be selected,depending on a particular purpose. An electric tube furnace isexemplified as a small apparatus.

More specifically, the above-described blend is put into a quartz tubethrough which an argon gas flows, and heated to a temperature between200° C. and 800° C. with the electric tube furnace to react for apredetermined time.

In the event that the heat CVD treatment is performed after the powdercomposed of silicon oxide or the silicon-silicon oxide composite isdoped with lithium, carbon reacts with silicon due to the influence ofthe doping lithium. The conductivity therefore decreases due to thegeneration of SiC, the cycle durability deteriorates due to excessivegrowth of the silicon crystal, and the battery characteristics thusdeteriorate. However, in the case of doping with lithium at a lowtemperature after coating with carbon like the present invention, thegeneration amount of SiC at the interface between the silicon-siliconoxide composite and the carbon coating and the growth of the siliconcrystal can be sufficiently suppressed, and the negative electrodematerial superior in the battery characteristics, such as the cycledurability, when used for a negative electrode can be obtained.

When the negative electrode material is used for a secondary batterywith a non-aqueous electrolyte, the negative electrode material for asecondary battery with a non-aqueous electrolyte can be thereforeobtained which has large discharge capacity and good cycle durability.In addition to this, low first efficiency, which is a fault of siliconoxide and the silicon-silicon oxide composite, is improved, in thenegative electrode material.

The negative electrode material for a secondary battery with anon-aqueous electrolyte obtained according to the present invention asabove can significantly contribute to the manufacture of an excellentnon-aqueous electrolyte secondary battery that has high capacity andgood first efficiency and is superior in the cycle durability,particularly a high performance lithium ion secondary battery, when usedfor the negative electrode active material of the non-aqueouselectrolyte secondary battery.

In this case, the obtained lithium ion secondary battery ischaracterized by the use of the above-described negative electrodeactive material, while the materials of the positive electrode, thenegative electrode, electrolyte, and separator, and the shape of thebattery are not restricted.

For example, the positive electrode active material to be used may betransition metal oxides, such as LiCoO₂, LiNiO₂, LiMn₂O₄, V₂O₅, MnO₂,TiS₂, and MoS₂, and chalcogen compounds.

For example, the electrolyte to be used may be lithium salts, such aslithium perchlorate, in a non-aqueous solution form. A non-aqueoussolvent to be used may be propylene carbonate, ethylene carbonate,dimethoxyethane, γ-butyrolactone and 2-methyltetrahydrofuran, alone orin admixture. Other various non-aqueous electrolytes and solidelectrolytes can be also used.

It is to be noted that when the negative electrode is fabricated byusing the above-described negative electrode material for a secondarybattery with a non-aqueous electrolyte, a conductive agent, such asgraphite, can be added to the negative electrode active material.

In this case, the type of conductive agent is not restricted inparticular, as long as it is an electronically conductive material thatdoes not cause decomposition and alteration in the manufactured battery.Specifically, the usable conductive agent includes metals in powder orfiber form, such as Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn and Si, naturalgraphite, synthetic graphite, various coke powders, meso-phase carbon,vapor phase grown carbon fibers, pitch base carbon fibers, PAN basecarbon fibers, and graphite obtained by firing various resins.

With regard to an additive amount of the above-described conductiveagent, the amount of the conductive agent contained in a blend of thenegative electrode material for a secondary battery with a non-aqueouselectrolyte according to the present invention and the conductive agentis desirably 1 to 60 mass % (more desirably 5 to 60 mass %, particularly10 to 50 mass %, more particularly 20 to 50 mass %).

When the additive amount of the conductive agent is 1 mass % or more, arisk of not being able to withstand expansion and contraction associatedwith charge/discharge can be avoided. In addition, when it is 60 mass %or less, a risk of a decrease in charge/discharge capacity can bereduced as much as possible.

When a carbon-based conductive agent is used for the negative electrode,the total amount of carbon in the negative electrode active material isdesirably 5 to 90 mass % (more desirably 25 to 90 mass %, particularly30 to 50 mass %).

When the total amount is 5 mass % or more, it can fully withstand theexpansion and contraction associated with charge/discharge. In addition,when the total amount is 90 mass % or less, the charge/dischargecapacity does not decrease.

EXAMPLES

Hereinafter, the present invention will be explained in more detail byshowing Examples and Comparative Examples. However, the presentinvention is not restricted to Examples below.

It is to be noted that in Examples below, “%” indicates “mass %”, and anaverage particle size is measured as a cumulative weight average value(or median diameter) D₅₀ upon measurement of particle size distributionby laser diffractometry. The size of silicon crystal is a size of acrystallite of Si (111) face, obtained by the Scherrer method from dataof the x-ray diffraction using Cu—Kα ray.

Example 1

Metallic silicon and silicon dioxide were blended at a molar ratio of1:1, and reacted at 1400° C. under a reduced pressure of 100 Pa togenerate a silicon oxide gas. The gas was cooled at 900° C. under areduced pressure of 50 Pa to precipitate, and a product in mass form wasconsequently obtained. The product was pulverized with a dry-type ballmill to obtain powder having an average particle size of 5 μm.

Chemical analysis revealed that the composition of this powder wasSiO_(0.95), the structure that silicon particles were dispersed tosilicon oxide in an atomic order and/or a crystallite state was observedwith a transmission electron microscope, and the powder was thussilicon-silicon oxide composite. The size of silicon crystal of thissilicon-silicon oxide composite was 4 nm.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment by using a raw material of a methane gas at 1100° C. under areduced pressure of 1000 Pa for 5 hours to coat the surface of thepowder with carbon. As a result, the carbon coating amount was 5% of thewhole powder including the coating.

Next, 2.7 g powder of lithium hydride (reagent made by Wako PureChemical Industries, Ltd) was put into a porcelain mortar having aninternal volume of 500 ml and pulverized in a glove box under a dry airatmosphere. Thereafter, 28.4 g silicon-silicon oxide composite powderhaving the carbon coating formed thereon was added thereto (lithiumhydride:silicon-silicon oxide composite (except carbon)=1:10 (a massratio)), and they were stirred and blended so as to be sufficientlyuniform.

The blend of 29 g was transferred to a 70 ml alumina boat and the boatwas carefully placed at the center of a furnace tube of an electric tubefurnace provided with an alumina furnace tube having an inner diameterof 50 mm. It was heated up to 600° C. at 5° C. every minute whilepassing an argon gas at 2 liters every minute, and was cooled afterholding of 1 hour.

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was8%. The structure that silicon particles were dispersed to silicon oxidein an atomic order and/or a crystallite state was observed with atransmission electron microscope.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 10 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratioof the peak intensity I(SiC) attributable to SiC of 2θ=35.8±0.2° to thepeak intensity I(Si) attributable to Si of 2θ=28.435 0.2° satisfied arelation of I(SiC)/I(Si)=0, when x-ray diffraction using Cu—Kα ray, andthus the generation of SiC was suppressed. The x-ray diffraction chartthereof is shown in FIG. 1.

Example 2

Except that lithium aluminum hydride was used as the lithium dopant inExample 1, the negative electrode material for a secondary battery witha non-aqueous electrolyte was manufactured in the same conditions asExample 1, and the same evaluation was carried out.

As a result, the doping amount of lithium was 2%. The structure thatsilicon particles were dispersed to silicon oxide in an atomic orderand/or a crystallite state was observed with a transmission electronmicroscope.

Moreover, it was confirmed that the peaks attributable to silicon,lithium silicate, and lithium aluminate were observed when the x-raydiffraction using Cu—Kα ray, the size of silicon crystal was 10 nm, andthus the growth of the silicon crystal was suppressed. It was furtherconfirmed that the ratio satisfied a relation of I(SiC)/I(Si)=0, andthus the generation of SiC was suppressed. The x-ray diffraction chartthereof is shown in FIG. 2.

Example 3

Metallic silicon and silicon dioxide were blended at a molar ratio of1:1, and reacted at 1400° C. under a reduced pressure of 100 Pa togenerate a silicon oxide gas. The gas was blended with a silicon gasthat was generated by heating metallic silicon to 2000° C. The blendedgas was cooled to 900° C. under a reduced pressure of 50 Pa toprecipitate, and a product in mass form was consequently obtained. Theproduct was pulverized with a dry-type ball mill to obtainsilicon-silicon oxide composite powder having an average particle sizeof 0.5 μm.

Chemical analysis revealed that the composition of this silicon-siliconoxide composite powder was SiO_(0.5), the structure that siliconparticles were dispersed to silicon oxide in an atomic order and/or acrystallite state was observed with a transmission electron microscope,and the powder was thus silicon-silicon oxide composite. The size ofsilicon crystal of this silicon-silicon oxide composite was 5 nm.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon at acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 except for a condition of lithiumhydride:silicon-silicon oxide composite (except carbon)=1:20 (a massratio).

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was5%. The structure that silicon particles were dispersed to silicon oxidein an atomic order and/or a crystallite state was observed with atransmission electron microscope, in the powder.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 14 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 4

Metallic silicon and silicon dioxide were blended at a molar ratio of1:1, and reacted at 1400° C. under a reduced pressure of 100 Pa togenerate a silicon oxide gas. The gas was blended with an oxygen gas ata molar ratio of 10:1. The blended gas was cooled to 900° C. under areduced pressure of 50 Pa to precipitate, and a product in mass form wasconsequently obtained. The product was pulverized with a dry-type ballmill to obtain silicon-silicon oxide composite powder having an averageparticle size of 5 μm.

Chemical analysis revealed that the composition of this silicon-siliconoxide composite powder was SiO_(1.5), the structure that siliconparticles were dispersed to silicon oxide in an atomic order and/or acrystallite state was observed with a transmission electron microscope,and the powder was thus silicon-silicon oxide composite. The size ofsilicon crystal of this silicon-silicon oxide composite was 3 nm.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon at acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 10 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 5

Metallic silicon and silicon dioxide were blended at a molar ratio of1:1, and reacted at 1400° C. under a reduced pressure of 100 Pa togenerate a silicon oxide gas. The gas was cooled to 600° C. under areduced pressure of 50 Pa to precipitate, and a product in mass form wasconsequently obtained. The product was pulverized with a dry-type ballmill to obtain powder having an average particle size of 5 μm.

Chemical analysis revealed that the composition of this powder wasSiO_(0.95), the structure that silicon particles were dispersed tosilicon oxide in an atomic order and/or a crystallite state was notobserved with a transmission electron microscope, and the powder wasthus silicon oxide (there is no disproportionation to silicon-siliconoxide). The diffraction peak of Si (111) face was not observed in thesilicon oxide, when the x-ray diffraction using Cu—Kα ray.

The silicon oxide powder was subjected to the heat CVD treatment in thesame conditions as Example 1 except for a treatment temperature of 800°C. and a treatment time of 120 hours, and the powder having the carboncoating formed thereon at a carbon coating amount of 5% was obtained.

Next, the powder having the carbon coating formed thereon was reactedwith lithium hydride in the same conditions as Example 1.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 1 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 6

Powder of the silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1 except for a treatmenttemperature of 1200° C. and a treatment time of 2 hours, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 23 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SIC)/I(Si)=0.019, and thus the generation ofSIC was suppressed.

Example 7

Powder of the silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1 except for a reaction temperature of 300° C. anda reaction time of 20 hours.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 9 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 8

Powder of the silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1 except for a reaction temperature of 800° C. anda reaction time of 10 minutes.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 25 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 9

Powder of the silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1 except for a condition of lithiumhydride:silicon-silicon oxide composite (except carbon)=1:100 (a massratio).

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was1%. The structure that silicon particles were dispersed to silicon oxidein an atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 8 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 10

Powder of the silicon-silicon oxide composite having a composition ofSiO_(1.5) and a silicon crystal size of 3 nm was obtained by the samemethod as Example 4.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1 except for a condition of lithiumhydride:silicon-silicon oxide composite (except carbon)=1:4 (a massratio).

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was16%. The structure that silicon particles were dispersed to siliconoxide in an atomic order and/or a crystallite state was observed with atransmission electron microscope, in the powder.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 30 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0.008, and thus the generation ofSiC was suppressed.

Example 11

Powder of the silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1 except for a treatmenttime of 1 hour, and the silicon-silicon oxide composite powder havingthe carbon coating formed thereon with a carbon coating amount of 1% wasconsequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 10 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0, and thus the generation of SiCwas suppressed.

Example 12

Powder of the silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1 except for a treatmenttime of 63 hours, and the silicon-silicon oxide composite powder havingthe carbon coating formed thereon at a carbon coating amount of 40% wasconsequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1.

The structure that silicon particles were dispersed to silicon oxide inan atomic order and/or a crystallite state was observed with atransmission electron microscope, in the negative electrode material fora secondary battery with a non-aqueous electrolyte obtained as above.

Moreover, it was confirmed that the peaks attributable to silicon andlithium silicate were observed when the x-ray diffraction using Cu—Kαray, the size of silicon crystal was 13 nm, and thus the growth of thesilicon crystal was suppressed. It was further confirmed that the ratiosatisfied a relation of I(SiC)/I(Si)=0.011, and thus the generation ofSiC was suppressed.

Comparative Example 1

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained. Thesize of silicon crystal of the silicon-silicon oxide composite was 7 nm.

The powder was used for a negative electrode material for a secondarybattery with a non-aqueous electrolyte without doping with lithium.

Comparative Example 2

Except that, in Example 1, the order of a heat CVD process (at atemperature of 1100° C., for 5 hours) and a process of doping withlithium (use of lithium hydride, lithium hydride:silicon-silicon oxidecomposite=1:10, a holing time of 1 hour at a temperature of 600° C.) wasreversed, a negative electrode material for a secondary battery with anon-aqueous electrolyte was manufactured in the same condition asExample 1, and the same evaluation was carried out.

It was revealed that the size of silicon crystal was 37 nm from theresult of the x-ray diffraction using Cu—Kα ray of the obtained negativeelectrode material for a secondary battery with a non-aqueouselectrolyte, and thus the growth of silicon crystal was considerablyaccelerated due to lithium.

It was confirmed that the ratio satisfied a relation ofI(SiC)/I(Si)=0.034, and thus SiC was largely generated. The x-raydiffraction chart thereof is shown in FIG. 3. In FIG. 3, a peakattributable to SiC is observed.

Comparative Example 3

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon with a carbon coating amount of 5% was consequently obtained.

Next, 28.4 g of the silicon-silicon oxide composite powder having thecarbon coating formed thereon was put into a 200 g glass jar and 2.7 gstabilized lithium powder SLMP made by FMC Corp. was further addedthereto, in a glove box under an argon atmosphere. It was blended bymanually shaking after putting the lid so as to be uniform.

The blend was put into an iron mortar having an internal volume of 1000ml, and was stirred with a pestle. At this point, ignition reaction withlight emission happened at the vicinity of a contact portion of asurface of the mortar with the pestle. Unreacted portions at theperiphery is thereupon moved thereon with a spatula so that thisreaction eventually prevailed uniformly throughout the mortar. After itwas sufficiently cooled, the product was fully disintegrate and takenout of the glove box.

It was revealed that the size of silicon crystal of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte obtained as above was 81 nm, and the silicon crystal waslargely grown.

Comparative Example 4

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon at a carbon coating amount of 5% was consequently obtained.

Next, 2.7 g powder of lithium hydroxide (reagent made by Wako PureChemical Industries, Ltd.) was put into a porcelain mortar having aninternal volume of 500 ml and pulverized in a glove box under a dry airatmosphere. Thereafter, 28.4 g of the silicon-silicon oxide compositepowder having the carbon coating formed thereon was added thereto, andthey were stirred and blended so as to be sufficiently uniform.

The blend of 29 g was transferred to a 70 ml alumina boat and the boatwas carefully placed at the center of a furnace tube of an electric tubefurnace provided with an alumina furnace tube having an inner diameterof 50 mm. It was heated up to 900° C. at 5° C. every minute whilepassing an argon gas at 2 liters every minute, and was cooled afterholding of 1 hour.

It was revealed that the size of silicon crystal of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte obtained as above was 68 nm, and the silicon crystal waslargely grown.

Comparative Example 5

Powder of a silicon-silicon oxide composite having a composition ofSiO_(0.3) was obtained by the same method as Example 3 except that thetemperature of heating metallic silicon was 2100° C.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon at acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 except for a condition of lithiumhydride:silicon-silicon oxide composite (except carbon)=1:20 (a massratio) to obtain a negative electrode material for a secondary batterywith a non-aqueous electrolyte.

Comparative Example 6

Powder of a silicon-silicon oxide composite having a composition ofSiO_(1.7) was obtained by the same method as Example 4 except that themolar ratio of a silicon oxide gas to an oxygen gas was 10:2.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon at acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 to obtain a negative electrode material for asecondary battery with a non-aqueous electrolyte.

Comparative Example 7

Silicon oxide powder (there is no disproportionation to silicon-siliconoxide) was obtained by the same method as Example 5.

The silicon oxide powder was subjected to the heat CVD treatment in thesame conditions as Example 1 except for a treatment temperature of 750°C. and a treatment time of 200 hours, and the powder having the carboncoating formed thereon at a carbon coating amount of 5% was obtained.

Next, the powder having the carbon coating formed thereon was reactedwith lithium hydride in the same conditions as Example 1 except for areaction temperature of 300° C. and a reaction time of 20 hours.

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was8%. It was revealed that the size of silicon crystal of the powder was0.4 nm, and the silicon crystal was not sufficiently grown.

Comparative Example 8

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1 except for a treatmenttemperature of 1350° C. and a treatment time of 40 minutes, and thesilicon-silicon oxide composite powder having the carbon coating formedthereon with a carbon coating amount of 5% was consequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the samecondition as Example 1.

It was revealed that the size of silicon crystal of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte obtained as above was 52 nm, and the silicon crystal waslargely grown.

Comparative Example 9

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon at acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was heated together with lithium hydride in thesame conditions as Example 1 except for a heating temperature of 100° C.and a heating time of 40 hours.

It was revealed that the doping amount of lithium of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte obtained as above was 0%, and thus the lithiation reactiondid not happen.

Comparative Example 10

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon with acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 except for a reaction temperature of 900° C. anda reaction time of 10 minutes.

It was revealed that the size of silicon crystal of the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte obtained as above was 85 nm, and the silicon crystal waslargely grown.

Comparative Example 11

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon with acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 except for a condition of lithiumhydride:silicon-silicon oxide composite (except carbon)=1:2000 (a massratio).

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was0.05%

Comparative Example 12

Powder of a silicon-silicon oxide composite having a composition ofSiO_(1.5) and having a size of 3 nm was obtained by the same method asExample 4.

The silicon-silicon oxide composite powder was subjected to the heat CVDtreatment in the same conditions as Example 1, and the silicon-siliconoxide composite powder having the carbon coating formed thereon with acarbon coating amount of 5% was obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 except for a condition of lithiumhydride:silicon-silicon oxide composite (except carbon)=2:5 (a massratio).

The doping amount of lithium of the negative electrode material for asecondary battery with a non-aqueous electrolyte obtained as above was23%

Comparative Example 13

Powder of a silicon-silicon oxide composite having a silicon crystalsize of 4 nm was obtained by the same method as Example 1.

This silicon-silicon oxide composite powder was subjected to the heatCVD treatment in the same condition as Example 1 except for a treatmenttime of 96 hours, and the silicon-silicon oxide composite powder havingthe carbon coating formed thereon at a carbon coating amount of 50% wasconsequently obtained.

Next, the silicon-silicon oxide composite powder having the carboncoating formed thereon was reacted with lithium hydride in the sameconditions as Example 1 to obtain a negative electrode material for asecondary battery with a non-aqueous electrolyte.

(Battery Evaluation)

The evaluation as the negative electrode active material for a lithiumion secondary battery was carried out by the following method/procedurewhich was common to all Examples and Comparative Examples.

A blend was first produced by adding flake synthetic graphite powder(average particle diameter D₅₀=5 μm) to 20 g of the obtained negativeelectrode material for a secondary battery with a non-aqueouselectrolyte in such amounts that the total of carbon in flake syntheticgraphite and the carbon coating formed on the negative electrodematerial for a secondary battery with a non-aqueous electrolyte was 42%.

Binder KSC-4011 made by Shin-Etsu Chemical Co., Ltd. was added in anamount of 10% as solids to the blend to form a slurry below 20° C.N-methylpyrrolidone was further added for viscosity adjustment. Thisslurry was speedily coated onto a copper foil having a thickness of 20μm and dried at 120° C. for 1 hour. An electrode was thereafter formedby pressing with a roller press and finally punched out so as to have asize of 2 cm² as the negative electrode. At this point in time, the massof the negative electrode was measured to calculate the mass of thenegative electrode material by subtracting the mass of the copper foil,flake synthetic graphite powder, and the binder therefrom.

To evaluate the charge/discharge characteristics of the obtainednegative electrode, a lithium-ion secondary battery for evaluation wasfabricated using a lithium foil as a counter electrode; using, as anon-aqueous electrolyte, a non-aqueous electrolyte solution obtained bydissolving lithium hexafluorophosphate in a 1/1 (a volume ratio) mixtureof ethylene carbonate and 1,2-dimethoxyethane at a concentration of 1mol/L; and using a polyethylene microporous film having a thickness of30 μm as a separator.

The fabricated lithium-ion secondary battery was allowed to standovernight at room temperature. Thereafter, with a secondary batterycharge/discharge test apparatus (made by Nagano, Co., Ltd.), the batteryfor evaluation was charged at a constant current of 1.5 mA until thetest cell voltage reached 5 mV at room temperature. After the voltagereached 5 mV, the battery was charged at a reduced current so that thecell voltage was maintained at 5 mV. When the current value haddecreased below 200 μA, the charging was terminated. The battery wasdischarged at a constant current of 0.6 mA, and the discharging wasterminated when the cell voltage reached 2.0 V.

The charge/discharge capacity per unit mass of the negative electrodematerial were calculated by subtracting the charge/discharge capacity ofthe flake synthetic graphite powder from the above-obtainedcharge/discharge capacity.

capacity per mass(mAh/g)=discharge capacity of negative electrodematerial(mAh)/mass of negative electrode material(g)

first efficiency(%)=discharge capacity of negative electrode materialmAh)/charge capacity of negative electrode material(mAh)×100

The charge/discharge test of the lithium-ion secondary battery forevaluation was carried out 50 times by repeating the charge/dischargetest as above, to evaluate the cycle durability.

capacity retention ratio (%)=discharge capacity of negative electrodematerial after 50 cycles (mAh)/first discharge capacity of negativeelectrode material (mAh)×100

Table 1 shows the result of evaluating the negative electrode materialfor a secondary battery with a non-aqueous electrolyte in Examples 1 to12 and Comparative Examples 1 to 13 by the above-described method.

TABLE 1 CAPACITY CAPACITY FIRST RETENTION PER MASS EFFICIENCY RATE(mAh/g) (%) (%) RESULT EXAMPLE 1 1370 85 89 GOOD EXAMPLE 2 1430 76 89GOOD EXAMPLE 3 1990 91 81 GOOD EXAMPLE 4 950 72 93 GOOD EXAMPLE 5 132083 90 GOOD EXAMPLE 6 1400 85 82 GOOD EXAMPLE 7 1360 85 89 GOOD EXAMPLE 81380 84 83 GOOD EXAMPLE 9 1480 73 89 GOOD EXAMPLE 10 850 95 90 GOODEXAMPLE 11 1420 85 85 GOOD EXAMPLE 12 870 85 93 GOOD COMPARATIVE 1500 6690 PARTICULARLY LOW EXAMPLE 1 FIRST EFFICIENCY COMPARATIVE 1320 84 35PARTICULARLY EXAMPLE 2 INFERIOR CYCLE DURABILITY COMPARATIVE 1380 87 58INFERIOR CYCLE EXAMPLE 3 DURABILITY COMPARATIVE 1170 74 63 INFERIORCYCLE EXAMPLE 4 DURABILITY COMPARATIVE 2310 97 54 INFERIOR CYCLE EXAMPLE5 DURABILITY COMPARATIVE 780 68 93 LOW CAPACITY EXAMPLE 6 COMPARATIVE1260 69 91 LOW FIRST EXAMPLE 7 EFFICIENCY COMPARATIVE 1390 86 66INFERIOR CYCLE EXAMPLE 8 DURABILITY COMPARATIVE 1500 66 89 PARTICULARLYLOW EXAMPLE 9 FIRST EFFICIENCY COMPARATIVE 1250 84 54 INFERIOR CYCLEEXAMPLE 10 DURABILITY COMPARATIVE 1490 69 90 LOW FIRST EXAMPLE 11EFFICIENCY COMPARATIVE 730 65 53 INFERIOR CYCLE EXAMPLE 12 DURABILITYCOMPARATIVE 690 85 93 LOW CAPACITY EXAMPLE 13

As shown in Table 1, it was revealed that the cases of the negativeelectrode materials in Examples 1 to 13 showed a good value of each ofthe capacity per mass, the first efficiency, the capacity retentionratio after 50 cycles (cycle durability), the cases where every one ofthe size of the silicon particles dispersed to silicon oxide in anatomic order and/or a crystallite state, the Si/O molar ratio, thecoating amount of the carbon coating with respect to the amount of thesilicon-silicon oxide composite, the doping amount of lithium withrespect to the amount of the silicon-silicon oxide composite,I(SiC)/I(Si) satisfied values of the present invention.

On the other hand, it was revealed that the case of Comparative Example1, where the doping with lithium was not performed, showed inferiorfirst efficiency, and that the case of Comparative Example 2, where thecarbon coating was formed after doping with lithium and the value ofI(SiC)/I(Si) exceeded 0.03, showed the cycle durability inferior to theother negative electrode materials and a large amount of SiC generation,whereas the capacity per mass and the first efficiency had no problem,and thus had characteristic problems for the negative electrodematerial.

Moreover, the cases of Comparative Examples 3 to 13 showed the followingresult. Since the doping with lithium was performed after coating withcarbon except for Comparative Example 9, where the lithiation reactiondid not happen, the generation of SiC was suppressed, and the cycledurability was superior to the case of Comparative Example 2 that is aconventional method. Since terms and conditions defined in the presentinvention were not satisfied, the cycle durability was inferior toExamples. Hereinafter, the cases will be individually explained.

In Comparative Example 3, where the lithium powder was used as thelithium dopant, silicon crystal particles were excessively grown due tothe ignition reaction in the process of doping with lithium, and thecycle durability thereby became inferior. The case of ComparativeExample 4, where lithium hydroxide was used as the lithium dopant,needed a high temperature for the doping treatment with lithium, therebythe size of silicon crystal contained in the negative electrode materialbecame too large, and the cycle durability consequently became inferior.

In Comparative Example 5, there was a shortage of oxygen (less than 0.5)in the silicon-silicon oxide composite, and thereby the cycle durabilitywas inferior. In Comparative Example 6, there was an excessive oxygen(more than 1.6), and thereby the capacity became low, whereas the cycledurability was good.

In Comparative Example 7, the growth of silicon crystal was insufficient(the size of the silicon particles was less than 0.5 nm), and therebythe first efficiency was low. In Comparative Example 8, the size of thecrystal was too large (the size of the silicon particles was more than50 nm), and thereby the cycle durability was inferior.

In Comparative Example 9, the heating temperature of the dopingtreatment with lithium was less than 200° C., thereby the lithiationreaction did not happen, and the first efficiency was low. InComparative Example 10, the heating temperature was more than 800° C.,thereby silicon crystal was largely grown, and the cycle durabilitybecame inferior.

In Comparative Example 11, the doping amount of lithium was low (lessthan 0.1 mass %) and thereby the first efficiency was low. InComparative Example 12, the doping amount of lithium was high (more than20 mass %), thereby the reactivity was high, there happened a troublewith adhesion to the binder when a battery was fabricated, and the cycledurability consequently became inferior.

In Comparative Example 13, the carbon coating amount was high (40 mass %or more), thereby the amount ratio of the silicon-silicon oxidecomposite doped with lithium was low, and thereby the capacity was low,whereas the cycle durability was good.

It is to be noted that the present invention is not restricted to theforegoing embodiment. The embodiment is just an exemplification, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept describedin claims of the present invention are included in the technical scopeof the present invention.

1. A negative electrode material for a secondary battery with anon-aqueous electrolyte comprising at least: a silicon-silicon oxidecomposite having a structure that silicon particles having a size of 0.5to 50 nm are dispersed to silicon oxide in an atomic order and/or acrystallite state, the silicon-silicon oxide composite having a Si/Omolar ratio of 1/0.5 to 1/1.6; and a carbon coating formed on a surfaceof the silicon-silicon oxide composite at a coating amount of 1 to 40mass % with respect to an amount of the silicon-silicon oxide composite,wherein at least the silicon-silicon oxide composite is doped withlithium at a doping amount of 0.1 to 20 mass % with respect to an amountof the silicon-silicon oxide composite, and a ratio I(SiC)/I(Si) of apeak intensity I(SiC) attributable to SiC of 2θ=35.8±0.2° to a peakintensity I(Si) attributable to Si of 2θ=28.4±0.2° satisfies a relationof I(SiC)/I(Si)≦0.03, when x-ray diffraction using Cu—Kα ray.
 2. Thenegative electrode material for a secondary battery with a non-aqueouselectrolyte according to claim 1, wherein a peak attributable to lithiumaluminate is further observed in the negative electrode material for asecondary battery with a non-aqueous electrolyte, when the x-raydiffraction using Cu—Kα ray.
 3. A lithium ion secondary battery havingat least a positive electrode, a negative electrode, and a non-aqueouselectrolyte having lithium ion conductivity, wherein the negativeelectrode material for a secondary battery with a non-aqueouselectrolyte according to claim 1 is used for the negative electrode. 4.A lithium ion secondary battery having at least a positive electrode, anegative electrode, and a non-aqueous electrolyte having lithium ionconductivity, wherein the negative electrode material for a secondarybattery with a non-aqueous electrolyte according to claim 2 is used forthe negative electrode.
 5. A method for manufacturing a negativeelectrode material for a secondary battery with a non-aqueouselectrolyte comprising at least: coating a surface of powder with carbonat a coating amount of 1 to 40 mass % with respect to an amount of thepowder by heat CVD treatment under an organic gas and/or vaporatmosphere at a temperature between 800° C. and 1300° C., the powderbeing composed of at least one of silicon oxide represented by a generalformula of SiO_(x) (x=0.5 to 1.6) and a silicon-silicon oxide compositehaving a structure that silicon particles having a size of 50 nm or lessare dispersed to silicon oxide in an atomic order and/or a crystallitestate, the silicon-silicon oxide composite having a Si/O molar ratio of1/0.5 to 1/1.6; blending lithium hydride and/or lithium aluminum hydridewith the powder coated with carbon; and thereafter heating the powdercoated with carbon at a temperature between 200° C. and 800° C. to bedoped with lithium at a doping amount of 0.1 to 20 mass % with respectto an amount of the powder.